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FAITH(4)                  OpenBSD Programmer's Manual                 FAITH(4)

     faith - IPv6-to-IPv4 TCP relay capturing interface

     pseudo-device faith [count]

     The faith interface captures IPv6 TCP traffic, for implementing userland
     IPv6-to-IPv4 TCP relay similar to faithd(8).

     Special action will be taken when IPv6 TCP traffic is seen on a router,
     and the routing table suggests routing it to the faith interface.  In
     this case, the packet will be accepted by the router, regardless of the
     list of IPv6 interface addresses assigned to the router.  The packet is
     captured by an IPv6 TCP socket, if it has the IN6P_FAITH flag turned on
     and it has matching address/port pairs.  Thus, faith allows captured IPv6
     TCP traffic to be relayed to some specific destination addresses.  User-
     land programs, such as faithd(8) can use this behavior to relay IPv6 TCP
     traffic to IPv4 TCP traffic.  The program can accept some specific IPv6
     TCP traffic, perform getsockname(2) to get the IPv6 destination address
     specified by the client, and perform application-specific address mapping
     to relay IPv6 TCP to IPv4 TCP.

     The IN6P_FAITH flag on an IPv6 TCP socket can be set by using
     setsockopt(2), with level set to IPPROTO_IPV6 and optname set to

     To handle error reports by ICMPv6, some of the ICMPv6 packets routed to
     the faith interface will be delivered to IPv6 TCP, as well.

     To understand how faith can be used, take a look at the source code of

     As the faith interface implements a potentially dangerous operation,
     great care must be taken when configuring the faith interface.  To avoid
     possible misuse, the sysctl(8) variable net.inet6.ip6.keepfaith must be
     set to 1 prior to use of the interface.  When net.inet6.ip6.keepfaith is
     0, no packet is captured by the faith interface.

     The faith interface is intended to be used on routers, not on hosts.

     inet(4), inet6(4), faithd(8)

     Jun-ichiro itojun Hagino, and Kazu Yamamoto, "An IPv6-to-IPv4 transport
     relay translator", RFC 3142, June 2001,

     The FAITH IPv6-to-IPv4 TCP relay translator first appeared in WIDE
     hydrangea IPv6 stack.

OpenBSD 3.4                     April 10, 1999                               1


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